| pmatch {base} | R Documentation |
pmatch seeks matches for the elements of its first argument
among those of its second.
pmatch(x, table, nomatch = NA, duplicates.ok = FALSE)
x |
the values to be matched: converted to a character vector by
as.character. |
table |
the values to be matched against: converted to a character vector. |
nomatch |
the value to be returned at non-matching or multiply partially matching positions. |
duplicates.ok |
should elements be in table be used more
than once? |
The behaviour differs by the value of duplicates.ok. Consider
first the case if this is true. First exact matches are considered,
and the positions of the first exact matches are recorded. Then unique
partial matches are considered, and if found recorded. (A partial
match occurs if the whole of the element of x matches the
beginning of the element of table.) Finally,
all remaining elements of x are regarded as unmatched.
In addition, an empty string can match nothing, not even an exact
match to an empty string. This is the appropriate behaviour for
partial matching of character indices, for example.
If duplicates.ok is FALSE, values of table once
matched are excluded from the search for subsequent matches. This
behaviour is equivalent to the R algorithm for argument
matching, except for the consideration of empty strings (which in
argument matching are matched after exact and partial matching to any
remaining arguments).
charmatch is similar to pmatch with
duplicates.ok true, the differences being that it
differentiates between no match and an ambiguous partial match, it
does match empty strings, and it does not allow multiple exact matches.
NA values are treated as if they were the string constant "NA".
A numeric vector of integers (including NA if nomatch =
NA) of the same length as x, giving the indices of the
elements in table which matched, or nomatch.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
Chambers, J. M. (1998) Programming with Data. A Guide to the S Language. Springer.
match, charmatch and
match.arg, match.fun,
match.call, for function argument matching etc.,
grep etc for more general (regexp) matching of strings.
pmatch("", "") # returns NA
pmatch("m", c("mean", "median", "mode")) # returns NA
pmatch("med", c("mean", "median", "mode")) # returns 2
pmatch(c("", "ab", "ab"), c("abc", "ab"), dup=FALSE)
pmatch(c("", "ab", "ab"), c("abc", "ab"), dup=TRUE)
## compare
charmatch(c("", "ab", "ab"), c("abc", "ab"))